어병세균종에 대한 Epidemiological cut-off value의 설정과 어류 장관 마이크로바이옴에 대한 항생제와 프로바이오틱스의 영향

Abstract

Use of antimicrobial agents is one of the most commonly used methods to treat bacterial diseases in fish farms. However, abuse of antibiotics could lead to the accumulation of residues as well as the emergence of antibiotic resistant bacteria. Aims of this study were to analyze non-wild type distribution of several bacterial fish pathogens based on epidemiological cut-off (ECOFF) values established in this study. Also, effects of antibiotics and probiotics administration on change in gut microbiota of olive flounder were determined using next generation sequencing. Antibiotic susceptibility testing based on an international protocol was conducted using some tens of strains of Streptococcus parauberis, Edwardsiella piscicida, Vibrio harveyi, Aeromonas salmonicida, and Phtobacterium damselae. Olive flounder were fed with feed supplemented with or without amoxicillin for 21days. Also, fish orally challenged with a non-wild type of E. piscicida were fed with or without a probiotic strain. Changes in gut microbiota were investigated in different timing points. In this study, ECOFF values were established for each fish pathogen against different antibiotics, which can be used as interpretive criteria for antibiotic disc diffusion test. Recent strains of S. parauberis and E. piscicida tend to be non-wild type (NWT) for more kinds of antibiotics. In case of V. harveyi, strains originated from farmed fish tend to be NWT for multiple antibiotics compared to wild-fish derived strains. In this study, amoxicillin seem to cause imbalance of fish gut microbiota (dysbiosis). Administration of probiotics could increase microbial diversity, indicating improve microbial balance in fish.